When is the addition of alum most effective in the treatment process?

The addition of alum is most effective at the start of the drinking water treatment process. Alum acts as a coagulant, helping to aggregate and remove fine particles and impurities from the water. When added early in the process, alum interacts with the suspended solids, enabling the formation of larger flocs that can be more easily removed during subsequent stages of treatment, such as sedimentation.

Adding alum at the beginning allows for optimal contact time with the contaminants before they are separated from the water, facilitating a more efficient coagulation process. As the treatment progresses through sedimentation and filtration, the floc particles bind together more effectively, contributing to clearer and cleaner water.

The other phases mentioned, such as the end of the process or during filtration and distribution, are not optimal for alum addition, as the coagulant needs sufficient time to react with the particles in the water, which would not be the case if added later in the treatment sequence.